Air flow and piston drive for pneumatic staplers



Jan. 27, 1959 H. w. JUlLFs 2,870,743

AIR FLOW AND PISTON DRIVE FOR PNEUMATIC STAPLERS Filed oct. e. 1954 RTTORNEYS.

UnitedStates Patent AIR FLOW AND PISTON DRIVE FOR yPNEUMATIC STAPLERS Howard W. Juilfs, Batavia, Ohio, assignor to Senco Products, Inc., Cincinnati, Ohio, a corporation of Ohio Application october 6, 1954, serial No. 460,667

1 Claim. (Cl. 121-21) My invention resides in the provision of novel means for admitting air into the cylinder behind the driving piston in order to actuate same and thereby drive the staple driver into contact with a staple so as to set it properly.`

Specically, my invention comprises an improvement over the arrangement shown in issued Patent No.` 2,585,940 entitled Valve Control System For Portable Pneumatic Staplers. In this latter patent there is shown and claimed an arrangement wherein air is brought behind the piston by means of a small longitudinal groove provided in the interior face -of the cylinder Wall. Although the arrangement of this patent has been generally satisfactory certain diliiculties have been experienced-including uneven wear of the cylinder wall and a limited driving power.

Accordingly, it is a specific object of my invention to provied an arrangement whichv insures a longer useful life for pneumatic staplers to which the invention is applied.

Another object of my invention is to provide a better and faster drive for the stapler.l

Yet another object of this invention is to provide for more consistent operation of tackers and staplers employing the invention.

Brietly, I accomplish these and other `objects of the invention which will become more apparent to those skilled in the art during the course of the following de` scription and from reference to the accompanying drawings by floating the piston centrallyof the cylinder within which it operates, the piston in a sense being air lubricated. The crux of this invention llies in introducing the air so that it will be distributed about the piston equally,` the` piston thus being'air-balanced.

All of the above will become more apparent from the following description and from the drawings in which like numerals are employed to designate like parts throughout and in which j Figure 1 is a side elevation of a pneumatic stapler or tacker employing the invention,

Figure 2 is a vertical section taken through the center of the tacker of Figure 1,

. Figure 3 is a fragmentary section corresponding tothe tacker of Figures 1 and 2 but showing the piston during a dilferent stage in its drive stroke.

Referring now to Figure 1, I have illustrated the. tacker or pneumatic stapler of this invention as comprising a handle section 10, a body 11, having a staple discharge nose 12 and a staple feed magazine 13. An air line has a swivel connection to the handle section as at 14 and there is a trigger 15 to actuate the valve 16 by which air is admitted from the chamber 17 of the handle 10 into the passageway 18. A spring 19 normally keeps the valve member 16 in the position shown in Figures 1 and 2 in which position the passageway 18 is opened to the exhaust chamber 20.

the springi24. As shown and claimed in United States Patent No. 2,671,214, I prefer that the piston 22 be recessed so as to receive not only the spring 24 but also l a member 25 to which the driver 26 is fastened, the driver 2(- and its member 25 being capable of longitudinal movement with respect to piston 22.

In the lower end of the tacker there is a resilient pad or cushion 27 against which the piston 22 will abut upon completion o'f its driving stroke. Because the driver 26 and its member 25 are free of the piston 22 such driver is free to advance under the inuence of inertia upon tinal stopping of the piston 22 by the cushion 27. A member 28 having an air vent therein aids in the formation of an air cushion to aid in the stopping of the piston 22 and this is also taught in Patent No. 2,671,214 as well as in other Juilfs patents.

The staple feed magazine 13 may include means upon which a strip of staples 29 may rest and be' urged to the drive track 30 by means of a spring-actuated follower 31. It will be understood that the particular feed magazine shown and thus briefly described does not constitute a limitation upon this invention. All that is needed is some sort of mechanism to insure a succession of staples being placed ahead of the driver 26 so that it may drive such staples through the track 30 into the work.

It is to be further understood that while I have shown l a preferred arrangement of the piston 22 and driver 26 The body 11 of the tacker defines a cylinder 21 in which the instant invention is not to be construed as limited only to this arrangement. It is quite possible and probable that the invention would apply equally as well to a stapler such as shown in Patent 2,682,052 wherein the.

driver andA its member 25 are fastened'to the piston 22 rather than free thereof as shown herein.

^ As stated above, in the prior patents referred to, a small longitudinal groove is provided in the interior face of vthe cylinder wall 21 which groove extends from the port 32 or terminus of the passage 18 to a point behind the piston when at rest against the head or cap 23. To this lend a suitable clearance or the like 33 is provided and this might consist merely of an extra thread of those which receive the cap or a protuberance might be given to the cap. In any event such a clearance 33 behind the piston 22 is also provided in the instant arrangement.

The critical difference between this invention and the arrangement discussed as employed in thepatents referred toresides in the elimination of the small groove and in the addition of an annular groove or recess 34 extending completely around the inner wall 'of the cylinder 21. This groove 34 corresponds in width substantially to that of the port 32 or the passage 18.

By eliminating the small groove above referred to and by employing in its stead the annular groove or passageway 34 I ensure that air introduced within the passageway 18 by manipulation of the trigger 15 contacts the piston on all sides substantially simultaneously. Air so introduced Within the groove 34 then seeps between the piston and cylinder wall. That air which moves towards the cushion 27 simply escapes from the device and that air which moves towards the cap 23 collects in the area 33 behind the piston so as to drive'same forwardly toward the cushion 27. I prefer that the distance from the passageway or groove 34 to the area 33 be shorter than the distance from such groove to the lower end of the piston 22 so that a bare minimum of air yis wasted. Air which collects in the area 33 acts to move the piston relatively slowly towards the cushion 27 until such time as it clears the port 32 of the passageway 18 whereuponfthe full strength of' the air will be active behind the piston so as to drive it rapidly towards the cushion 27.

Formerly, in those devices which employed the small groove referred to, after some time there was a noticeable wear on that portion of the cylinder wall opposite the passage 18'since the air striking the piston initially acted against one' side thereof only. This resultedin the piston being forced away from the cylinder entrance port and` small i longitudinal groove. agains.A the.opp,osite cylinderwall thus creating a drag onthepiston. andwear inthe cylinder'. In this mannerth'ell piston was.also slowed in its movement. in aditionair escaped inwary-V ing degreepthus makingthe op`,erat-ion...of,theY device, especially after' prolonged use,v somewhat inconsistent.k

By introducing the air'aboutlallsides of the-piston substantially simultaneously as-is accomplished by providing ythe groove 34, the' piston 22"-.is air-balanced, that is such piston is floated within the centerof .the cylinder 21'. Since the dlag'abovereferred .to isthus eliminated lthe'pis'ton will travel lat agreaterspeed even lthough the air pressures used are identical'andeven though the Staplers used are the same exceptA for thissubstitution of the annular groove34fo'r the small longitudinal groove formerly employed.l The drivingv power is so improved, for example, that a pneumatic tacker,V which formerly could drive only a half-inch stapleunder a givenair press'ure can now drive a ,ve-eighths. inch staple under the same pressure. This' is a .considerable improvement for it enables theuse of the same model tackers and standard airpr'essures to accomplishthe driving of diierent size staples as is often demanded by various jobs.. Thus instead of employing two or more different lines .and sizes of tackers one suchtacker will suice for a greater number of needs.

The operation` of .the device embodying my invention is as follows. squeezing` of the trigger 1S against the valve member 16 in opposition to the spring 19` opens` the passageway 18;."to' airl from the chamber17.- This air owingin. the; passageway 13 is introduced :within the circulargrooye or channel'34`provided-in the interior face ofthe cylinder wall' '21,' this'channel 34 filling with air so that the piston 22`s completelysurrOUndedthereby.

Irithi'smanner'the piston is fioa'ted air ,and is air-` b'alanced'.' Air seeps from the channel 34 andcollects behind the piston .2`2'in the region of the clearance 33..

Air thus building upjin back'of the piston 22 will cause such piston to move forwardly in the direction of the bumper 27.v When the piston has moved suciently to pass the port 32"-1eading from the channel 18- to the groove 34 the full 'pressure of the air introduced within the device .is then behind the piston 22 with the result that it is driven hardl 'and fast towards the bumper 27.

As the piston is'rnoved in the manner just described the driver 26 will' contact a staple 29 brought into4 position within the drive track 30 by thefe'ed mechanism 173 and` follower 31. This driverftvillforce such staplel through the nose 12 into the work being stapled.. Movement .of the drive'pisto'n 22 is slowed upby ,the air. cushionwhich ,builds upl ahead of the piston. 22.and..which isA controlled by the member 28,'iinal 'stoppingoi the-.piston .occurringy when it 'strikes the ,bumper 27. Thespring 24 returns. thegdriver and piston to the positiont of. Figure .2,where-y upon another pull of the' trigger 15.will cause arepeat of'.

the operations just described.' y v It is` to be understood'that vall ofthe actions. just de'- scribed in connection withY the driving of the piston take place extremely rapidly, This makes it that much more important that air be introduced within the cylinder 21 by means of the channel.34 above described for this insures consistent operation of the piston 22 and much longer life of the staple gun or tacker since there is no uneven wear. Balancing the piston centrally of the cylinder as is accomplishediby introducing the air completely about the'fpiston .not only insuresy a longer life for the tacker and more consistent operation' but it also results in a better drive and increased power. These advantages are realized by introducng'the air within the annular groove or "channel 134 'and this, as stated; constitutes the crux of the instant. invention.

It will be understoodby those skilled in the art that certain modicationsmay *befmadegin' the invention disclosed without departing from its scope and spirit and although I have shown the invention as embodied in certain. structure -I .donot 4intencl tonbelimitedy tov such structure except in-V so..far asit.isaspecifically'setfforth,in the subjoined claim.. Obviously other.feed mechanismsand driving .arrangements can be made vwithout departingy from` the principal teachingof introducingftheair on all. sides of the` piston as is accomplished by the annular groove.

o1 channel 34.

Having l.thus described my-inventionv what I claim as new and what Idesire to .protect byway of United States Letters Patent is:

In a pneumatic stapling machine havingffa staple driver actuatedby a solid-wall piston reciprocating within a cylinder. having a cylinder head,.saicl piston` being driven by air andreturned byaz spring, said piston at rest abutting said'head, said cylinder and saidheadproviding. aA

clearance behind said piston ;at rest, and said machine includinga. trigger actuated :valve controlling the admis-- sion of ain tolsaid cylinder, the-improvement; which comprises: an :annular groove Vextending. completely around the inner wall of said cylinder., `saidgroove beingspaced.

from said clearancefsaid groove beingpositio'ned in-that partof said .cylinder .occupied by said 4piston at` rest where-- by said'groove is covered by said piston atrest, and an` air .passageway extending from said valve to said annular groove whereby air is uniformly' distributcdabout the periphery of said piston, said annular groove constituting the entire means in said cylinder wall for the passage of airfromsaid valve to said clearance,'air fromsaid groove. beingfree toseep evenly between` the periphery of said.`

solid-wall piston and said cylinder ,wall' to said clearance e whereby said piston is airbalancedwithin the center of said cylinder and drag of said piston jagainst said cylinder wall isV eliminated, air` which seeps between said solidwall piston and said cylinder/.wall away fromsaid clearance being free toiexhaust, whereby pressureis builtup in said clearance behind said piston to lmove saidxpiston fl'omsaid head onthe drive strokey of saidsaidpiston.`

References. Cited inI thele of. this vpatent UNITED STATES.PATENTS 25,087,138 Brick". July, 1.3, 1937 2,101,159 Stevens' Dec. 7', 1937Av 2,585,940 .lulifs Feb. 19,1952'v 2,590,155 Cannon Mar. 25, 1952 

